1. Field of the Invention
This invention relates to an analogue dynamic memory circuit for storing analogue signal wave forms which vary in amplitude over time and from which the stored signal wave forms can be read out sequentially and repeatedly.
2. Prior Art Statement
A memory circuit capable of storing analogue signal wave forms which varies over time can be utilizing a time delay element and a feedback loop, as shown in FIG. 2.
This memory circuit is constituted by connecting the output side of a time delay element 1 to the input side thereof via a feedback line 2. The time delay element 1 can be a system with a magnetic recording tape drive head and a reproducing head separated by a certain distance or, alternatively can be a CCD consisting of a plurality of serial charge store cells. When a CCD is used, the analogue signal is transferred from cell to cell in synchronization with a clock signal.
The reference numeral 3 designates a gate circuit which opens for a time period shorter than the delay time to of the delay element 1 and allows an analogue signal to enter from an input terminal 4.
The analogue signal input in this way circulates via feedback line 2 and is thus stored in the feedback loop, which includes the delay element 1.
This circulating analogue signal can be read out sequentially from an output terminal 5. If the feedback loop gain is unity then, theoretically, the signal is stored permanently.
However, when the circulation of an analogue signal is continued over a long period of time in this kind of circuit, the following problems are found to occur.
Although this memory circuit is isolated from the outside by a gate circuit, the quality of the stored analogue signal is degraded by noise or signal sources existing in the loop circuit.
One shot single pulses aside, all repetitive wave forms can be represented as the sum of the sinusoidal wave of the fundamental frequency and the sinusoidal waves of the higher harmonics (i.e. integer multiples) of the fundamental frequency.
Among these sinusoidal waves, those which have frequencies equal to integer multiples of the inverse of the delay time of the analogue dynamic memory system are amplified as tuned waves as the analogue signals circulate in the feedback loop. This makes it impossible to utilize the kind of feedback circuit shown in FIG. 2 in practical applications.
The purpose of this invention is to solve this kind of tuned wave increase problem.